12 



HARD WICKE '5 5 CI EN CE-GO SSIF. 



the inclination of the ray is changed, it leaning now 

 from left to right. When the umbrella is rotated at 

 a moderate pace, the two edges of each gore, aided 

 by the persistence of vision, produce a sort of St. 

 Andrew's Cross. The inclination of the rays is seen 

 to be produced by the tightly-stretched and curved 

 threads that run from rib to rib. In fig. 105 two gores 

 are roughly shown here, while the light is seen 

 through the centre of gore A ; where the minute 

 portions of the threads are horizontally arranged, the 

 ray is necessarily vertical. When the light is seen 

 through the silk at y, the threads there being inclined 

 from the horizontal, the ray produced is likewise in- 

 clined from the vertical. The threads in gore B, at 

 the part x, having an inclination opposite to those 

 at y, the luminous ray has, therefore, a similarly 

 opposite inclination to that formed previously. 



On advancing close to a lamp, and pointing the 

 ferule of the umbrella exactly towards the light, a 

 star is seen, one ray of which extends down each 

 gore of the umbrella ; so that the star has as many 

 rays as there are gores. This star revolves as the 

 umbrella is rotated. A fainter set of luminous lines 

 at right angles to each ray of the star may be observed, 

 these being formed by the threads that run in the 

 direction of the length of the umbrella. They do not 

 form so bright a line, because they are not quite 

 parallel, and are further apart from one another than 

 the cross threads. 



These instances, I think, may serve to show that 

 it is not necessary to conceive that the crystals of 

 Phlogopite exert, because of their crystalline nature, 

 any refractive influence, thus causing the phenomenon 

 described. It naturally occurs to one to explain 

 similarly the rays seen proceeding from points of 

 light when these are looked at with half-closed eyes. 

 But, on examining the rays thus formed, they are 

 seen to form either a confused, many-pointed star, 

 or more usually a long line of light stretching above 

 and below the flame ; that is, in a direction parallel 

 with the intervening eyelashes (the supposed cause 

 of the phenomenon), instead of at right angles to 

 them, as one would have expected from the previous 

 examples. So that we are obliged to seek some other ex- 

 planation in this case. The true explanation was pointed 

 out by Mr. Arnulph Mallock in the August number 

 of Nature. These effects are produced by small, 

 prism-like tear-fihus, situated at the upper and lower 

 angles formed by the eyelid and the eye, the effects 

 being due to refraction in this case. When two 

 Phlogopite films are rotated one behind the other, 

 both stars are distinctly seen, the rays of one alter- 

 nately coinciding and falling between those of the 

 otlier. 



I forward you a mounted slide of each variety of 

 Phlogopite. I have a few other specimens, should 

 any of your readers care to exchange. 



A. W. Stokes. 



Labcraloiy, Guy s Hospital. 



MICROSCOPY. 



False Light Excluder. — The Amer'uan N'atii- 

 ralist states that Mr. E. Gundlach mounts his new 

 two-inch lenses with a brass tube five-eighths of an 

 inch long, projecting below the front surface of the 

 objective, and having a perforated diaphragm at its 

 lower end. This cuts off much of the stray light 

 that would otherwise enter, and still leaves one inch 

 and an eighth of working focus. 



Sydenhamand Forest Hill NaturalHistory 

 AND Microscopical Club (founded 1871). — The 

 objects of this club are the reading of papers and 

 exhibition of specimens in all branches of Natural 

 History and Microscopy. It meets on tlie first 

 Thursday in each month at the Foresters' Hall ; 

 Forest Hill, at 8 p.m.: first excursion during the 

 summer months on Saturday afternoon. Annual 

 subscription, 5^. President, Mr. Edward Simpson ; 

 Hon. Sec, Mr. E. L. C. P. Hardy. 



Vorticell^.— In a bottle I have had standing 

 by me for some time I found some fungoid growths 

 at the bottom, to which were attached several vor- 

 ticella; ; they were very minute, and had long, thin, 

 and very slender footstalks ; but the peculiarity about 

 them was, that one and all of them were living 

 singly, and not in colonies, as I have seen in others. 

 Is this characteristic of a distinct species ? One in- 

 dividual had the power of bringing the head down, 

 by bending the footstalk at an exceedingly sharp 

 angle midway between the point of attachment and 

 the bottom of the bell ; this it did several times, and 

 always bent it at the same place. Can any of your 

 readers tell me what species of vorticellrc this is ? — 

 F. B. 



Parasites on Cyclops. — Several specimens of 

 the Cyclops, which I have at present, are quite 

 crowded with the bell-shaped parasite "A. H." writes 

 about in the February number of Science-Gossip. 

 I counted on one poor unfortunate upwards of eighty 

 individuals, and not one part of his body, except the 

 antennce, was free of them ; even the eye-spot had 

 two upon it. They are very long in the body, com- 

 paratively speaking, and have no spiral stalk, but 

 otherwise are similar to vorticella;. — P. B. 



Mounting in Damar. — Having read Mr. E. B. 

 L. Brayley's article on the above subject, I should 

 like to be permitted to ask one or two questions. 

 1st. How air-bubbles are to be prevented from 

 forming within an object when placed upon a hot 

 slide without any medium? It seems to me that the 

 heat soon fills the object with air, unless it is kept 

 moist with turps or benzole : and secondly, does not 

 the Japan varnish ever run into the damar when 

 there is no other varnish between ? I have been 

 accustomed to use damar with heat as Mr. Brayley 

 does, with this exception, viz., that I first heat the 



